This invention pertains to a multi-mode hydro-mechanical transmission shift system utilizing the displacement position of a variable displacement component of a hydrostatic unit of the transmission to initiate mode changes and having a control circuit with a plurality of valves providing reliability and resistance to nuisance reshifting.
Previous multi-mode hydromechanical transmissions have used differential speed sensing to initiate mode shifts and such systems have been subject to error and reliability problems. Some of the previous systems have also used a time delay to prevent nuisance reshifts when under heavy load at vehicle speeds near the shift point.
The prior art also discloses hydromechanical transmissions having two modes of operation wherein the displacement position of a variable displacement unit or component of a hydrostatic unit is used to initiate mode changes. However, this prior art does not disclose a transmission having three or more modes of operation with mode changes being responsive to the position of the displacement control.